Alcohol fuel is known as an alternate fuel for gasoline and light diesel oil (hereunder referred to as a regular fuel). An operation of an internal combustion engine must be changed in response to whether a regular fuel or a fuel mixture of the regular fuel and the alternate fuel is injected from a fuel injector.
If it is attempted to obtain an excess air ratio equal to gasoline with respect to an alcohol fuel, a larger amount of fuel injection than gasoline (for example about 1.6 times) is required. That is, with regard to the output torque of an internal combustion engine obtained by fuel injection for a certain period of time, the output torque obtained in the case of the injection of a fuel mixture is smaller than that in the case of the injection of a fuel containing gasoline by 100%. Consequently, the injection time of a fuel mixture must be longer than that of 100% gasoline.
As stated above, in order to control an internal combustion engine to a desired operational state, information on whether the injected fuel is a regular fuel or a fuel mixture (hereunder referred to as fuel feature information) is required. JP-2007-120414A shows an internal combustion engine is controlled by installing an alcohol concentration sensor to detect an alcohol concentration in a fuel tank. However, an alcohol concentration sensor is expensive and the cost largely increases accordingly.